// This file is part of OpenTSDB.
// Copyright (C) 2010-2012  The OpenTSDB Authors.
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 2.1 of the License, or (at your
// option) any later version.  This program is distributed in the hope that it
// will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty
// of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
// General Public License for more details.  You should have received a copy
// of the GNU Lesser General Public License along with this program.  If not,
// see <http://www.gnu.org/licenses/>.
package net.opentsdb.core;

import java.util.NoSuchElementException;

import net.opentsdb.core.Aggregators.Interpolation;

/**
 * A function capable of aggregating multiple {@link DataPoints} together.
 * <p>
 * All aggregators must be stateless. All they can do is run through a sequence
 * of {@link Longs Longs} or {@link Doubles Doubles} and return an aggregated
 * value.
 */
public abstract class Aggregator {

    /** Interpolation method this aggregator uses across time series */
    private final Interpolation interpolation_method;

    /** String name of the aggregator */
    private final String name;

    /**
     * Create a new instance of this class.
     * 
     * @param interpolationMethod
     *            The interpolation method to use.
     * @param name
     *            The name of this aggregator.
     */
    protected Aggregator(final Interpolation interpolationMethod, final String name) {
        this.interpolation_method = interpolationMethod;
        this.name = name;
    }

    /**
     * A sequence of {@code long}s.
     * <p>
     * This interface is semantically equivalent to {@code Iterator<long>}.
     */
    public interface Longs {

        /**
         * Returns {@code true} if this sequence has more values. {@code false}
         * otherwise.
         */
        boolean hasNextValue();

        /**
         * Returns the next {@code long} value in this sequence.
         * 
         * @throws NoSuchElementException
         *             if calling {@link #hasNextValue} returns {@code false}.
         */
        long nextLongValue();

    }

    /**
     * A sequence of {@code double}s.
     * <p>
     * This interface is semantically equivalent to {@code Iterator<double>}.
     */
    public interface Doubles {

        /**
         * Returns {@code true} if this sequence has more values. {@code false}
         * otherwise.
         */
        boolean hasNextValue();

        /**
         * Returns the next {@code double} value in this sequence.
         * 
         * @throws NoSuchElementException
         *             if calling {@link #hasNextValue} returns {@code false}.
         */
        double nextDoubleValue();

    }

    /**
     * Aggregates a sequence of {@code long}s.
     * 
     * @param values
     *            The sequence to aggregate.
     * @return The aggregated value.
     */
    public abstract long runLong(Longs values);

    /**
     * Aggregates a sequence of {@code double}s.
     * 
     * @param values
     *            The sequence to aggregate.
     * @return The aggregated value.
     */
    public abstract double runDouble(Doubles values);

    /**
     * Returns the interpolation method to use when working with data points
     * across time series.
     * 
     * @return The interpolation method to use
     */
    Interpolation interpolationMethod() {
        return interpolation_method;
    }

    @Override
    public String toString() {
        return name;
    }
}
